The present invention relates to a novel insecticidal composition comprising a microcapsule wherein diazinon or chlorpyrifos is made a core substance and a polycationic water-soluble nitrogen-containing compound such as gelatin and a hardener are made a wall substance.
Further, it relates to a microcapsule-containing composition comprising microcapsules mentioned above, surfactant to prevent the microcapsules from coagulating each other and a thickener, and also to a novel insecticidal composition consisting of a stable microcapsule-containing composition which is obtained by granulating the microcapsule-containing composition above with a filler.
U.S. Pat. No. 2,800,457 discloses that an oleaginous material is formed into a microcapsule by the complex-coacervation method, and the separation of the microcapsule is conducted by filtration or centrifugal separation method. In general, there is a spray drying process as a method usually used when a material contained in a solution or dispersion is taken out from it as dry powders. However, according to this method, the wall film tends to be porous resulting in a defect that the core material can not be sufficiently formed into capsule, since the drying of the wall film is conducted in a short time. Furthermore, a microcapsule obtained by U.S. Pat. No. 2,800,457 is not a single core but a multiple core and the coagulation among microcapsules is noticed resulting in a defect to cause clogging of spray nozzle when sprayed.
Japanese published examined patent application No. 17433/1973 discloses that the hardening of a gelatin wall substance in the microencapsulation process occurs in an acidic solution; however, the reactivity for hardening reaction in an acidic solution is poor. The microcapsule is unstable and is easily solidified, since a cationic surfactant is used in order to prevent microcapsules produced from coagulation, and the surfactant is left unchanged in the microcapsule after drying. Further, there is reported the use of a cationic or an anionic surfactant to prevent microcapsules from coagulation due to the attachment of them with the rapid increase in the viscosity; however, these surfactants are easily dissociated in an acidic or an alkaline solution and unstable, and cause remarkable foaming. Also there is a fear that an anionic surfactant forms water-insoluble salts in hard water. Though a cationic surfactant has a high sterilizing effect, on the other hand, it reacts with a cellulosic disintegrator used when granulated and solidifies when preserved over a long period of time. The microcapsule has a defect of poor dispersion in water due to a binder and a thickener which are added in order to improve properties of dry powders.